Step 2) Line a 12-hole (2-1/2 inch) muffin tin with cup cake liners or spray muffin cups generously with cooking spray.
Step 3) Combine flour, sugar, espresso powder, baking powder, baking soda and salt in a large mixing bowl. Stir with fork to thoroughly blend ingredients; set aside.
Step 4) Heat chocolate over very low heat in small saucepan until melted; remove from heat.
Step 5) Whisk buttermilk, oil, eggs and vanilla until smooth. Add to flour mixture; stir until combined. Batter will be thick. Fold in melted chocolate and miniature chips, if desired. Divide evenly into prepared pan.
Step 6) Bake for 20 to 25 minutes or until toothpick inserted into the center comes out clean. Remove from oven; cool on wire rack completely before frosting.
Frosting:
Mix powdered sugar, espresso powder and cocoa powder in a mixing bowl until thoroughly combined.
Beat in butter, milk and vanilla with an electric mixer. Frosting will be thick, but smooth and spreadable.